In recent years, reconfigurable integrated circuit devices attract attention. A typical example of the reconfigurable integrated circuit devices is a field programmable gate array (hereinafter referred to as “FPGA”). The FPGA realizes basic logical information using logical blocks, and changes connections among the logical blocks using switches. Using the logical blocks and the switches, a user can realizes arbitrary logical functions in the FPGA. A lookup table circuit (hereinafter referred to as “LUT circuit”) which realizes an arbitrary truth table is used for such a logical block. The LUT circuit is provided with a configuration memory and a multiplexer, and reads a state of a memory selected by an input signal. The arbitrary truth table can be realized by rewriting the configuration memory.
An SRAM (Static Random Access Memory) is often used as a configuration memory. The SRAM can be manufactured by the same process as a logic transistor so that the SRAM type memory is easy to be manufactured. However, the SRAM type memory is a volatile memory and data is lost when power is turned off. Accordingly, it is necessary to keep the power of the LUT circuit turned on. Further, with advance of miniaturization of semiconductor devices, leakage current of the SRAM increases. As a result, leakage current of an LUT circuit miniaturized using most advanced processes increases.